1. Field of the Invention
The present invention relates to an airbag device mountable on a vehicle, and more particularly, relates to an airbag device which is provided with a limitation member that constrains a part of the airbag from unfolding and deploying at airbag deployment.
2. Description of Related Art
JP 2008-272360 A and JP2001-287611 A (especially, FIG. 13) disclose a known airbag device which includes a holding member that constrains (regulates) a part of an airbag from unfolding and deploying and let other part of the airbag be deployed first. In the airbag device, the holding member is configured to temporarily hold opposite end regions (front and rear end regions or left and right end regions) of the airbag which is folded up and housed in a housing such that the opposite end regions are held from unfolding for an instant in an initial stage of airbag deployment and thereafter freed from the holding member and deployed.
In the above specified prior art references, the holding member is a part of a wrapping member which wraps up the airbag for keeping the airbag in a folded-up configuration. The wrapping member is formed into a parallelepiped box having a shape retention property, and opposite end regions of the wrapping member serve as the holding member. Between the holding members at opposite end regions of the wrapping member is an opening which the airbag gets out of at airbag deployment. The holding member constrains the opposite end regions of the airbag from unfolding and deploying until a peripheral region of the opening are deformed in an arcuate fashion and the opposite end regions of the airbag slip out of the holding members.
However, since the holding members itself have a shape retention property and are secured to a part of the airbag device having rigidity, the holding members are not easily deformable and accordingly sometimes fail to release the held regions of the airbag smoothly so the airbag can be deployed quickly.
JP 2010-158914 A discloses an airbag device which includes an airbag in a folded-up configuration and a wrapping member wrapped around the airbag. The airbag device further includes a flap member which is so deployable as to contact with an abnormally-seated vehicle occupant (i.e., a vehicle occupant situated too close to the airbag device, or more specifically, to an airbag housing) at airbag deployment so as to prevent the occupant from contacting the airbag too early in the course of airbag deployment.
However, it is uncertain whether this configuration will help constrain a part of the airbag from unfolding and deploying temporarily in a steady fashion since the flap member is mounted on the wrapping member which is flexible and tearable.